No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Degradation of tyrosol by a novel electro-Fenton process using pyrite as heterogeneous source of iron catalyst
Abstract
Tyrosol (TY) is one of the most abundant phenolic components of olive oil mill wastewaters. Here, the degradation of synthetic aqueous solutions of 0.30 mM TY was studied by a novel heterogeneous electro-Fenton (EF) process, so-called EF-pyrite, in which pyrite powder was the source of Fe(2+) catalyst instead of a soluble iron salt used in classical EF. Experiments were performed with a cell equipped with a boron-doped diamond anode and a carbon-felt cathode, where TY and its products were destroyed by hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton's reaction between Fe(2+) and H2O2 generated at the cathode. Addition of 1.0 g L(-1) pyrite provided an easily adjustable pH to 3.0 and an appropriate 0.20 mM Fe(2+) to optimize the EF-pyrite treatment. The effect of current on mineralization rate, mineralization current efficiency and specific energy consumption was examined under comparable EF and EF-pyrite conditions. The performance of EF-pyrite was 8.6% superior at 50 mA due to self-regulation of soluble Fe(2+) by pyrite. The TY decay in this process followed a pseudo-first-order kinetics. The absolute rate constant for TY hydroxylation was 3.57 × 10(9) M(-1) s(-1), as determined by the competition kinetics method. Aromatic products like 3,4-dihydroxyphenylethanol, 4-hydroxyphenylacetic acid, 4-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid and catechol, as well as o-benzoquinone, were identified by GC-MS and reversed-phase HPLC. Short-chain aliphatic carboxylic acids like maleic, glycolic, acetic, oxalic and formic were quantified by ion-exclusion HPLC. Oxalic acid was the major and most persistent product found. Based on detected intermediates, a plausible mineralization pathway for TY by EF-pyrite was proposed.
Copyright © 2015 Elsevier Ltd. All rights reserved.
... However, it also acted as an effective catalyst at other pH values to degrade organic compounds, such as amoxicillin [20], aniline [21], chloramphenicol, and metronidazole [22]. In particular, natural pyrite (FeS 2 ) effectively catalyzed the degradation of a synthetic azo dye [23], levofloxacin [24], tyrosol [25], and sulfamethazine [26] by adjusting the pH of the solution to suitable values for the EF process. Heidari et al. (2021) compared the efficiencies of naturally occurring minerals chromite (FeCr 2 O 4 ), chalcopyrite (CuFeS 2 ), and ilmenite (FeTiO 3 ) as catalysts in the oxidation of the antibiotic cefazolin by the EF process, and it was determined that the chalcopyrite structure was more effective than the others [27]. ...
... Heidari et al. (2021) compared the efficiencies of naturally occurring minerals chromite (FeCr 2 O 4 ), chalcopyrite (CuFeS 2 ), and ilmenite (FeTiO 3 ) as catalysts in the oxidation of the antibiotic cefazolin by the EF process, and it was determined that the chalcopyrite structure was more effective than the others [27]. The use of pyrite and chalcopyrite acted as buffers and regulated the pH of the medium in the range of 3-4 depending on the catalyst dosage, according to the Equations (6)-(9) [23,25,26] O), and pyrite (FeS 2 ), as natural sources of iron in the heterogeneous electro-Fenton process for the degradation of gemcitabine [28]. The authors obtained their optimum results with a pyrite catalyst. ...
A weak aspect of the electro-Fenton (EF) oxidation of contaminants is the dependence of the Fenton reaction on acidic pH values. Therefore, the rationale of this work was to develop a novel catalyst capable of promoting the EF oxidation process at near-neutral and basic pH values. In this framework, rhombohedral FeCO3 was synthesized hydrothermally and used as a catalyst in the EF oxidation of p-benzoquinone (BQ). The catalyst was characterized using various surface and spectroscopic methods. Moreover, the effects of applied current (100–500 mA), time (1–9 h), catalyst dosage (0.25–1.00 g L−1), and initial concentration of BQ (0.50–1.00 mM) on the total organic carbon removal efficiency were determined. The results indicated that a 400 mA current was sufficient for a 95% total organic carbon removal and that the increase in catalyst dosage had a positive effect on the mineralization of BQ. It was determined that at pH 3, FeCO3 behaved like a homogeneous catalyst by releasing Fe3+ ions; whereas, at the pH range of 5–7, it shifted to a homogeneous/heterogeneous catalyst. At pH 9, it worked solely as a heterogeneous catalyst due to the decrease of Fe ions passing into the solution. Finally, the spent catalyst did not undergo structural deformations after the EF treatment at higher pH values and could be regenerated and used several times
... 35 to 37). The additionally generated Fe 2+ ions favored the •OH production and process efficiency by the Fenton reaction, as explained in Eq. 38 [47,48,49] ...
The current study focused on the charge and mass transport effect on the continuous electro-Fenton (EF) process treatment of synthetic Reactive orange 16 (RO16) dye using low-cost stainless-steel electrodes and sodium chloride (NaCl) supporting electrolytes, respectively. Lab-scale experiments were carried out in a 500 mL volume reactor cell at various initial RO16 dye concentrations (75-250 mg/L) and flow rates (0.05-0.4 L/h). The results showed that the decolorization rate increased quantitatively with an increment of the RO16 dye concentration and flow rate due to the mass transport limitation. Increasing the mass flow rate increased the mass transfer coefficient (km), improving the kinetics of the decay. It was found that regardless of inflow concentrations, the dye removal efficiency increased with the flow rate. Additionally, the degradation rate, elimination capacity, current efficiency (CE), and specific energy requirement were estimated for the process. A dimensionless current density relation was generated for the developed continuous stirred tank to describe the kinetics and mass transfer relationship towards the overall reaction rate contribution. It was found that the stainless-steel anode electrode proved to be preferable due to lower energy consumption (6.5 kWh m-3) and less iron sludge production. Additionally, the application of pyrite (FeS2) particulate electrode increased the process efficiency (~ 5%) for TOC removal and current mineralization while maintaining its sustainability for reuse.
... However, nZVI faces challenges in achieving uniform dispersion in water due to its weak van der Waals forces, high surface energy, and strong intrinsic magnetic interactions. These factors limit its interaction with pollutants and overall usability [14]. Researchers have employed carriers such as activated carbon [15], clay [16], and biochar [17] to address the aforementioned challenges. ...
... However, the use of pyrite in the Fenton process requires careful consideration of the environmental conditions and the presence of other minerals in the system to ensure its effectiveness as a catalyst. Ammar et al. used pyrite to decompose tyrosol in the electro-Fenton process and obtain about 90% mineralization of solutions [79][80][81]. ...
... Insoluble minerals such as pyrite (FeS 2 ), chalcocite (Cu 2 S), bornite (Cu 5 FeS 4 ), goethite (-FeOOH), magnetite (Fe 2 O 3 ), hematite (-Fe 2 O 3 ), ferrihydrite (Fh), and wüstite (FeO) had been used to get rid of natural contaminants satisfactorily (Usman et al. 2018). Trichloroethylene, diclofenac, pyrene, and toluene have all been found to be degraded using pyrite as a heterogeneous catalyst under the Fenton technique (Ammar et al. 2015). Kantar et al. (2019) utilized pyrite as a catalyst packed in a column reactor to purify real pharmaceutical effluent below dynamic situations. ...
... It is widely used in chemical industries, such as industries of photographic products, drugs, lubricants, dyes, etc. [217,218]. CC can be generated during the decomposition of aromatic compounds in Fenton process [181,219] and it is the first intermediate generated during tyrosol degradation in an electro-Fenton process [181,220]. CC is released to the environment via several sources: paper and pulp, pharmacy, textile, paint, insecticides, pharmaceutical, oil refinery, etc. [221]. It is one of the most abundant phenolic compounds in OMW [178]. ...
... Second, the pyrite-activated persulfate (pyrite-PMS) system based on Formula (9) promotes the generation of SO •− 4 radicals to oxidize organic pollutants [27,28]. Recently, an electro-Fenton system using pyrite (pyrite-EF) as a catalyst has been used to degrade organic pollutants such as antibiotics [29,30], tyrosol [31], etc. However, pyrite has limitations such as insufficient dispersibility and surface reactivity, slow dissolution, limited efficiency of heterogeneous reactions at the solid-liquid interface, and low catalytic activity [32]. ...
The use of natural pyrite as a catalyst for the treatment of recalcitrant organic wastewater by an electro-Fenton system (pyrite-EF) has recently received extensive attention. To improve the catalytic activity of natural pyrite (Py), magnetic pyrite (MPy), and pyrrhotite (Pyr), they were obtained by heat treatment, and the nanoparticles were obtained by ball milling. They were characterized by X-ray diffraction, X-ray electron spectroscopy, and scanning electron microscopy. The degradation performance of rhodamine B (Rhb) by heterogeneous catalysts was tested under the pyrite-EF system. The effects of optimal pH, catalyst concentration, and current density on mineralization rate and mineralization current efficiency were explored. The results showed that the heat treatment caused the phase transformation of pyrite and increased the relative content of ferrous ions. The catalytic performance was MPy > Py > Pyr, and the Rhb degradation process conformed to pseudo-first-order kinetics. Under the optimum conditions of 1 g L−1 MPy, an initial pH of five, and a current density of 30 mA cm−2, the degradation rate and TOC removal rate of Rhb wastewater reached 98.25% and 77.06%, respectively. After five cycles of recycling, the chemical activity of MPy was still higher than that of pretreated Py. The main contribution to Rhb degradation in the system was •OH radical, followed by SO4•−, and the possible catalytic mechanism of MPy catalyst in the pyrite-EF system was proposed.
... photo-Fenton process) and the use of solid ironcontaining catalysts (e.g. pyrite) to tackle the abovementioned issues (Ammar et al., 2015). ...
PAHs are largely spread in the aquatic environment, and the drawbacks of conventional remediation techniques as well as the expenditures for alternative disposal of polluted sediments lead to seek more effective, environmentally–friendly and sustainable approaches. Therefore, the present review shows a critical overview of the literature evaluated with VOSviewer, focusing on the problem of PAH–contaminated marine sediments and the knowledge of available remediation processes to shed light on what research and technology lack. This review supplies specific information about the key factors affecting biological, physical–chemical and thermal remediation techniques, and carefully examines the drawbacks associated with their employment for remediating PAH–polluted marine sediments by showing adequate alternatives. The technologies thoroughly discussed here are biostimulation, bioaugmentation, sediment washing, carbonaceous adsorbent addition and thermal desorption. The environmental and economic impacts associated with the application of the mentioned remediation technologies have been also taken into account. Finally, this review examines new research directions by showing future recommendations.
... 14 In recent years, there has been great interest in the development of catalytic cathodes for HEF by physically coating catalyst powder onto carbon materials, such as pyrite, goethite, and hematite. 15,16 When the active catalyst component is fixed on the cathode and applied in the electro-Fenton system, it can produce H 2 O 2 at the cathode while producing ROS in situ, 17 which reduces the resistance of mass transfer and the cost of catalyst recovery. For example, Xu et al. developed a carbon cloth with polypyrrole (PPy)-encapsulated needle-like Fe 2 O 3 nanoarrays (PPy@N-Fe 2 O 3 @CC) as an EF cathode for the degradation of 10 mg L −1 roxarsone. ...
BACKGROUND
It would be highly advantageous to develop a heterogeneous electro‐Fenton (HEF) system in which the catalyst is fixed to recycle easily and the electrode itself can produce and activate H2O2 simultaneously. In this study, a new sandwich‐like bifunctional cathode using carbon cloth (CC) loaded with FeOCl nanoparticles and activated carbon fiber (ACF) was fabricated and used in the HEF process for the degradation of antibiotic trimethoprim (TMP).
RESULTS
Experimental results showed that the activated carbon fiber and FeOCl‐modified carbon cloth cathode (ACF/CC@FeOCl) exhibited a promising catalytic performance to reduce O2 to generate H2O2 on the surface of ACF and activate H2O2 to generate hydroxyl radicals (•OH) at the active sites of FeOCl nanoparticles, thus enabling a rapid TMP degradation in a wide pH range (3–9). Various influencing factors, such as applied cathodic current, pH and TMP concentration, were investigated, and the optimal condition was found at 0.36 A, pH 3.0, and 100 mg L⁻¹ TMP, where 99.7% TMP was degraded within 90 min and 74.4% total organic carbon (TOC) was removed within 360 min. Under the condition of 0.36 A and initial pH 6.8, 100 mg L⁻¹ TMP was completely degraded within 120 min and the mineralization efficiency could achieve 61.5% within 360 min. The coumarin fluorescence probing technique and radical quenching experiments revealed that •OH was the predominant reactive oxygen species (ROS) in the ACF/CC@FeOCl‐HEF process.
CONCLUSION
The reusability and stability tests showed that the ACF/CC@FeOCl cathode has excellent performance and good stability, and this is very promising for the efficient degradation of refractory organic pollutants in the HEF process. © 2022 Society of Chemical Industry (SCI).
... HEF system avoids the formation of iron sludge and is beneficial to the reuse of catalyst [13]. In general, iron bearing minerals [14][15][16], iron or iron oxide-based composites [17,18] and iron-based functionalized cathode materials [19][20][21][22], have been used as the most popular EF catalysts. However, traditional iron minerals are faced with the problems of high metal iron leaching and easy aggregation. ...
Heterogeneous electro-Fenton (HEF) technology has become a hot topic for degradation of organic pollutants in water. However, it remains a challenge to design effective catalysts for high H2O2 utilization and pollutant degradation. In this work, we explored a novel iron and nitrogen-doped carbon catalyst derived from hemin (Fe-N-C) using KHCO3-MgO as dual-porogen. The results suggested that the KHCO3-MgO dual-porogen could not only improve the porous characteristics of catalyst, but also expose iron sites and change the proportion of nitrogen species. The pollutant degradation results demonstrated that the Fe-N-C-700/HEF system exhibited high ciprofloxacin degradation efficiency of 93.82% within 50 min and mineralization efficiency of 87.87% within 90 min by low energy consumption. Moreover, cycle experiments and metal ions leaching experiments revealed that the catalyst had good stability and recyclability. Electron spin resonance (ESR) test and radical capturing experiment showed that •OH was the dominant active species in this HEF system. In addition, the Fe-N-C-700/HEF system achieved satisfactory performance in the treatment of real water matrix, indicating the possibility for practical application in wastewater purification.
... Furthermore, recently AOPs as an environmentally friendly method received extraordinary attention because of their high efficiency for removing nonbiodegradable organic pollutants from aquatic environments, such as wastewater, ground, and surface water by the in-situ generation of the •OH as the oxidizing agent. Among the AOPs, the Fenton reagent (mixture of H 2 O 2 and Fe 2+ ion) has attracted significant attention due to its strong oxidative capacity on organic contaminants 8,9 . The main disadvantages of using the electro-Fenton (EF) process in water and wastewater treatment are, on the one hand, dependence on electrical energy and, on the other hand, the management of the produced sludge and also the neutralization of the treated effluent after the process. ...
Introduction: Perchloroethylene (PCE) is one of the most well-known chlorinated organic compounds recently detected in aqueous environments. The presence of PCE in aquatic ecosystems has caused many health problems and environmental challenges. Therefore, its removal and treatment from aqueous environments are essential.
Materials and Methods: The electro-Fenton (EF) process was carried out in a cylindrical reactor containing 250 mL contaminated water with PCE. The effects of parameters, including solution pH (3-12), current density (2-10 mA cm-2), H2O2 concentration (20-70 µL H2O2 per 250 mL sample.), PCE concentration (5-50 mg L-1), and electrolysis time (1-15 min) on PCE degradation were investigated. The kinetics and radical’s scavenger of the EF process were examined to detect the exact mechanism of PCE degradation.
Results: The degradation of the PCE of 98.1% was obtained in the optimum condition, including solution pH of 5, the current density of 8 mA cm-2, H2O2 concentration of 50 µL per 250 mL sample, PCE concentration of 15 mg L-1, and electrolysis time of 10 min. The kinetics studies of the EF process indicated that the obtained results were in satisfactory agreement with the first-order model (R2 = 0.9858, Kapp = 0.2822). Also, the addition of ethanol and tertiary butanol caused an inhibiting effect.
Conclusion: The EF process was effectively applied to degrade PCE from polluted water as an efficient technique. The obtained results indicated that the generation of •OH throughout the EF process was the key mechanism that controlled the EF process.
... The feed water comprises 0.05 M of Na 2 SO 4 , 0.2 mM of FeSO 4 .7H 2 O, and the target organic contaminants based on their optimum performance in previous studies (Ammar et al., 2015;Xie et al., 2016a). The pH of the feed solution was set to 3.0 by using 0.01 M H 2 SO 4 and a pH meter (Hach 8,506,000 Portable) (Liu and Sun, 2007a). ...
Advanced oxidation processes can remove emerging contaminants from wastewater with complete degradation; however, the slow kinetics of the degradation process and extensive energy input hinder further commercialization. We developed a hybrid process, comprising electro-Fenton and membrane distillation, to simultaneously degrade organic pollutants and extract pure water from the mixture. Methyl orange, as a synthetic dye, and ibuprofen, as an emerging pharmaceutical contaminant, were used to study the effectiveness of the electro-Fenton/membrane distillation hybrid system. The dye degradation studies were conducted in three modes: electro-Fenton at room temperature, electro-Fenton at high temperatures, and electro-Fenton coupled with membrane distillation. The hybrid process showed 99% dye removal and 92% total organic carbon decay of an initial 20 ppm methyl orange after 6 hours of operation. The mineralization current efficiency at room temperature was approximately 50%, which was increased by 5 and 10 times for high-temperature electro-Fenton and hybrid electro-Fenton/membrane distillation, respectively. The hybrid process also reduced the energy consumption based on the specific energy consumption results. The liquid chromatography-multiple reaction monitoring was used for quantitative profiling of ibuprofen degradation with a concentration of 0.5 ppm. The electro-Fenton/membrane distillation (20–60) removed 94% of ibuprofen after 3 hours compared to the 74.7% removal rate by electro-Fenton (60).
... Insoluble minerals such as pyrite (FeS 2 ), chalcocite (Cu 2 S), bornite (Cu 5 FeS 4 ), goethite (α-FeOOH), magnetite (Fe 2 O 3 ), hematite (α-Fe 2 O 3 ), ferrihydrite (Fh) and wüstite (FeO) have been successfully applied in the removal of organic pollutants [15,44]. More specifically, the use of pyrite as a heterogeneous catalyst in the Fenton process has been reported for the degradation of trichloroethylene, diclofenac, pyrene and toluene [45]. Kantar et al. [46] used pyrite as a catalyst packed in a column reactor for purification of real effluent from the pharmaceutical industry under dynamic conditions. ...
Nowadays, water pollution is one of the most dangerous environmental problems in the world. The presence of the so-called emerging pollutants in the different water bodies, impossible to eliminate through conventional biological and physical treatments used in wastewater treatment plants due to their persistent and recalcitrant nature, means that pollution continues growing throughout the world. The presence of these emerging pollutants involves serious risks to human and animal health for aquatic and terrestrial organisms. Therefore, in recent years, advanced oxidation processes (AOPs) have been postulated as a viable, innovative and efficient technology for the elimination of these types of compounds from water bodies. The oxidation/reduction reactions triggered in most of these processes require a suitable catalyst. The most recent research focuses on the use and development of different types of heterogeneous catalysts, which are capable of overcoming some of the operational limitations of homogeneous processes such as the generation of metallic sludge, difficult separation of treated water and narrow working pH. This review details the current advances in the field of heterogeneous AOPs, Fenton processes and photocatalysts for the removal of different types of emerging pollutants.
... Hydrogen peroxide (H 2 O 2 ) is a powerful and versatile environmental-friendly oxidant, widely used in synthesis of organic compounds, pulp bleaching, and wastewater treatment (Gierer and Jansbo, 1993;Kato et al., 2013;Mondal et al., 2018;Xu et al., 2018) for degradation of harmful organic waste. Due to its strong oxidation selectivity, H 2 O 2 is converted into more oxidative ⋅OH in various advanced oxidation processes (AOPs) (Ammar et al., 2015), which can effectively mineralize most organic pollutants into CO 2 , H 2 O and inorganic ions, making AOPs a promising method for removing difficult-to-degrade organic pollutants in the aqueous environment. The currently practicing method for the synthesis of high concentration H 2 O 2 is the anthraquinone oxidation (AO) process (Campos-Martin et al., 2006;Kraft, 2008). ...
Electrocatalytic reduction of O2 is an environmentally friendly method for H2O2 production. Design and fabrication of efficient non-metallic electrocatalytic gas diffusion cathode (GDC) with strong durability is highly desirable. Carbon nanotubes (CNTs) is a promising electrocatalytic material for 2-electron O2reduction but with unsatisfying electrocatalytic activity and stability. Hetero-atom doping of CNTs has been proved to promote its electrocatalytic selectivity for H2O2 generation, but the electrocatalytic performance of CNTs co-doped with two hetero-atoms and its synergy mechanisms need further investigation. Herein, O or F mono-doped and O/F co-doped CNTs with different O/F ratios were developed through one-step acidification and then used as the electrocatalysts on the graphite felt (GF) GDC for H2O2 generation. The electrocatalytic activity was greatly improved by the synergetic effects of O/F-containing functional groups on the surface of CNTs. The GF/CNTs-1:1 cathode with the highest contents of COOH and CFX (X ≥ 2) was found to be most efficient in H2O2electrogeneration at a wide pH range of 1–9. Further, with coating of polytetrafluoroethylene (PTFE) film, the GF/CNTs-1:1/PTFE-30 GDC exhibited extremely high activity and superior stability in 15 cycles without aeration, giving the maximum H2O2 yield of 263.2 mg·L⁻¹in 1 h with little decline rate. The present study provides opportunities for developing highly efficient, cost effective, and durable metal-free electrocatalysts for H2O2 evolution.
... Among metalbased catalysts (Ti, Al, Fe, etc.), natural iron-based minerals have attracted noticeable attention due to their accessibility, cost efficiency, non-toxicity and environment friendly (Expósito et al., 2007). Many kinds of iron-based mineral catalysts, including pyrite (Barhoumi et al., 2016;Ammar et al., 2015), chalcopyrite (Barhoumi et al., 2017) martite (Khataee et al., 2016b), hematite , magnetite have been employed as the heterogeneous catalysts in various AOPs. Among mentioned catalysts, α-FeOOH with a high density of hydroxyl groups and thermodynamically stable Fe (III) oxide, has shown an acceptable performance in various wastewater treatment processes (Liu et al., 2014). ...
Plasma-treated goethite nanoparticles with high surface area and improved density of surface hydroxyl groups were synthesized from natural goethite (NG) using Argon (PTG-Ar) and Nitrogen (PTG-N 2) as plasma environment to enhance the performance of heterogeneous catalytic ozonation process. Synthesized samples were characterized by FESEM, EDX, TEM, XRD, XPS, BET-BJH, FTIR, AAS and pH PZC. Results indicated a significantly different morphology for the prepared samples with negligible change in crystal structure. Furthermore, the catalytic activity and synergy factor of the NG and PTG nanocatalysts were evaluated for degradation and mineralization of Sulfasalazine antibiotic (SSZ) as an environmental hazardous contaminant. The highest removal efficiency was achieved 96.05 % under the optimal operating conditions. The kinetic study confirmed the pseudo-first-order reaction for the degradation process. Moreover, the dissolved ozone concentration and effect of organic and inorganic salts were studied in order to assess the reactive oxidant species (ROSs) and catalyst active sites in the process. The mechanism investigation showed the catalytic ozonation of SSZ was mainly performed by successive attacks of hydroxyl radicals (•OH), superoxide radicals (% O 2 −) and direct ozone molecules. Environmentally-friendly modification of the NG, negligible iron leaching, successive reusability and superior catalytic activity are the major benefits of the PTG nanoparticles.
Looking at modern approaches to catalysis, this volume reviews the extensive literature published on this area. Chapter highlights include Fenton chemistry, advanced manufacturing in heterogeneous catalysis, membrane reactors for light alkane dehydrogenation, and new insights and enhancement of biocatalysts for biomass conversion in the bioproducts industry.
Appealing to researchers in academia and industry, the detailed chapters bridge the gap from academic studies in the laboratory to practical applications in industry, not only for the catalysis field, but also for environmental protection. The book will be of great benefit to any researcher wanting a succinct reference on developments in this area now and looking to the future.
Nowadays, toxic/persistent organic micropollutants generated from different human activities contaminate natural water streams since conventional water and wastewater treatment plants remain inefficient to eliminate these pollutants. Alternatively, advanced oxidation processes (AOPs) constitute an efficient and environment friendly techniques to remove these pollutants from water and wastewater effluents. These processes are based on in situ generation of strong oxidants, like hydroxyl radicals, that are able to oxidize organic pollutants up to their mineralization. The Fenton process, which is based on the Fenton’s reagent (a mixture of hydrogen peroxide and ferrous iron), is one of the first AOPs. To enhance the efficiency of the Fenton process, several improvements have been achieved in recent years. This chapter focuses on the fundamental characteristics of this process and overviews Fenton-based processes such as photo-Fenton, electro-Fenton, and related processes as well as anodic Fenton and Fered-Fenton processes, including their application to the treatment of contaminated waters.
In this study, the selective adsorption of aromatic compounds on mesoporous MIL-53(Al) was investigated, and followed the order: Biphenyl (Biph) > Triclosan (TCS) > Bisphenol A (BPA) > Pyrogallol (Pyro) > Catechol (Cate) > Phenol (Phen), and exhibited high selectivity toward TCS in binary compounds. In addition to hydrophobicity and hydrogen bonding, π-π interaction/stacking predominated, and more evidently with double benzene rings. TCS-containing halogens could increase π interaction on the benzene rings via forming Cl-π stacking with MIL-53(Al). Moreover, site energy distribution confirmed that complementary adsorption mainly occurred in the Phen/TCS system, as evidenced by ΔQpri (the decreased solid-phase TCS concentration of the primary adsorbate) < Qsec (the solid-phase concentrations of the competitor (Phen)). In contrast, competitive sorption occurred in the BPA/TCS and Biph/TCS systems within 30 min due to ΔQpri = Qsec, followed by substitution adsorption in the BPA/TCS system, but not for the Biph/TCS system, likely attributed to the magnitude of energy gaps (Eg) and bond energy of TCS (1.80 eV, 362 kJ/mol) fallen between BPA (1.74 eV, 332 kJ/mol) and Biph (1.99 eV, 518 kJ/mol) according to the density-functional theory of Gaussian models. Biph with a more stable electronic homeostasis than TCS lead to the occurrence of substitution adsorption in the TCS/BPA system, but not in the TCS/Biph system. This study provides insight into the mechanisms of different aromatic compounds on MIL-53(Al).
Rapid industrial development has led to excessive levels of various contaminants in natural water, which poses a challenge to the innovation of environmental remediation technology. In recent years, iron sulfide and its modified materials have attracted extensive attention in environmental remediation due to their high activity in advanced oxidation processes and widespread existence in anoxic environment. This paper reviewed the latest advances of the synthesis methods for iron sulfide and modified FeS. In addition, the application of persulfate activation by iron sulfide materials (FeS, FeSx, S−ZVI, FeS@Carbon materials and MFexSy) for contaminants remediation is also reviewed, and the enhancement of this system by photo irradiation, ultrasound, and microwave have also been concluded. Additionally, the interaction mechanism of iron sulfide and persulfate with contaminants was reviewed. Based on the above contents, we concluded that the long−term stability of iron sulfide, the toxicity to organisms of iron sulfide materials in the treated water, and the combination of FeS/PS with other assisted technologies should be focused in future.
Due to the high dependence on the pH of influent water and the level of ferrous species, the applicability of the electro-Fenton (EF) system is poor. A highly applicable dual-cathode (DC) EF system with self-adjusting pH and ferrous species is proposed: gas diffusion electrode (GDE) for generation H2O2 and Fe/S doped multi-walled carbon nanotubes (Fe/S-MWCNT) modification active cathode (AC) for adjusting pH and iron species. The strong synergistic enhancement effect between two cathodes (synergy factor up to 90.3%) improves the catalytic activity of this composite system about 12.4 times higher than that of cathode alone. Impressively, AC has the ability of self-regulate to shift towards the optimal Fenton pH (around 3.0) without adding reagents. Even pH can be adjusted from 9.0 to 3.4 within 60 min. This characteristic gives the system a wide range of pH applications, while avoiding the disadvantage of the high cost of traditional EF in pre-acidification. Furthermore, DC has a high and stable ferrous species supply, and the iron leaching amount is about twice less than that of heterogeneous EF system. Long-term stability of the DC system and its easy activity regeneration exhibit the potential of environmental remediation in industrial application.
Hydroxytyrosol, one of the most powerful natural antioxidants, exhibits certificated benefits for human health. In this study, a biomimetic approach to synthesize hydroxytyrosol from the hydroxylation of tyrosol was established. EDTA-Fe2+ coordination complex served as an active center to simulate tyrosine hydroxylase. H2O2 and ascorbic acid were used as oxygen donor and hydrogen donor, respectively. Hydroxy radical and singlet oxygen contributed to active species. The biomimetic system displayed analogous component, structure, and activity with TyrH. Hydroxytyrosol titer of 21.59 mM, and productivity of 9985.92 mg·L-1·h-1 was achieved with 100 mM tyrosol as substrate. The proposed approach provided efficient and convenient route to quickly produce high amount of hydroxytyrosol.
Developing effective and highly stable Heterogeneous electro-Fenton (HEF) catalysts for removing organic pollutants from aquatic environments is a challenge in the scientific world. In this study, activated carbon/Goethite/Fe3O4/ZnO was synthesized as a novel eco-friendly and economic HEF catalyst to remove chemical oxygen demand (COD) from woolen textile wastewater (WTW). According to characterization analyses, the catalyst was in a polycrystalline structure, had good stability (-34.53 mV), and had an average pore diameter was 8.017 nm. According to catalytic activity results, COD removal by anodic oxidation (AO) was 44.29%, AO-H2O2 was 58.99%, and adsorption was 18.5%. ⋅OH and ⋅O2– responsible for COD removal with 76.21% and 28.07%. The low p-value (<0.0001), high F-value (456.90), high Adeq. the precision value (76.74) and high R² (0.9977) of the model show that the established quadratic model is significant, valid, successful in estimating data, and reliable in navigating design space. Optimal conditions were determined as aeration rate: 2.86 L/min, current density: 5.38 mA/cm², catalyst dose: 0.194 g/L, reaction time: 85.41 min. COD removals were determined experimentally and theoretically as 96.39% and 98.66%. The total cost was $ 1.75 to remove 1 kg COD from WTW. The synthesized catalyst showed good performance over five cycles (82%), suggesting its use on an industrial scale. © 2023 The Korean Society of Industrial and Engineering Chemistry
Natural iron-bearing minerals are widely distributed in the environment and show prominent catalytic performance in pollutant removal. This work provides an overview of groundwater restoration technologies utilizing heterogeneous electro-Fenton (HEF) techniques with the aid of different iron forms as catalysts. In particular, applications of natural iron-bearing minerals in groundwater in the HEF system have been thoroughly summarized from either the view of organic pollutant removal or degradation. Based on the analysis of the catalytic mechanism in the HEF process by pyrite (FeS2), goethite (α-FeOOH), and magnetite (Fe3O4) and the geochemistry analysis of these natural iron-bearing minerals in groundwater, the feasibility and challenges of HEF for organic degradation by using typical iron minerals in groundwater have been discussed, and natural factors affecting the HEF process have been analyzed so that appropriate in situ remedial measures can be applied to contaminated groundwater.
The efficient catalytic activity and strong durability possibility of carbon-based three-dimensional fiber materials remains an important challenge in Electro-Fenton advanced oxidation technology. Graphite felt (GF) is a promising electrode material for 2-electron oxygen reduction reaction but with higher catalytic inertia. Anodizing modification of GF has been proved to enhance it electro-catalytic property, but the disadvantages of excessive or insufficient oxidation of GF need further improved. Herein, the surface reconstituted graphite felt by anodizing and HNO3 ultrasonic integrated treatment was used as cathode to degrade norfloxacin (NOR) and the substantial role of different modification processes was essentially investigated. Compared with the single modification process, the synergistic interaction between these two methods can generate more defective active sites (DASs) on GF surface and greatly improved 2-electron ORR activity. The H2O2 can be further co-activated by Fe2+ and DASs into •OH(ads and free) and •O2- to efficiently degrade NOR. The treated GF with 20 min anodizing and 1 h HNO3 ultrasound had the highest electrocatalytic activity in a wide electric potential (-0.4 V to -0.8 V) and pH range (3-9) in system and the efficient removal rate of NOR was basically maintained after 5 cycles. Under optimal reaction conditions, 50 mg L-1 NOR achieved 93% degradation and almost 63% of NOR was completely mineralized within 120 min. The possible NOR degradation pathways and ecotoxicity of intermediates were analyzed by LC-MS and T.E.S.T. theoretical calculation. This paper provided the underlying insights into designing a high-efficiency carbon-based cathode materials for commercial antibiotic wastewater treatment.
Catalytic performances and leaching behavior of 9 natural iron minerals as heterogeneous electro-Fenton catalysts for the treatment of imidacloprid wastewater were studied. The results showed that magnesioferrite exhibited the best catalytic ability among these minerals with UV absorbance at 270 nm (UV270) removal of 49.11% and COD removal of 83.59% within 4 h using graphite cathode and Ti/(RuO2)0.88-(IrO2)0.12 anode at initial pH 3 with a catalyst dose of 5 g/L, a current density of 40 mA/cm² and an electrode spacing of 2 cm. The instantaneous current efficiency (ICE) at 4 h and energy consumption (EC) reached 2.30% and 2.20 kWh/gCOD respectively. It was found that the components contained in natural iron minerals, such as Al, alkali metal (K) and alkaline earth metals (Mg, Ca, Ba), would dissolve into the electrolyte solution, raising the final pH to 6.5-8.5 and ultimately reducing the reaction efficiency. Except magnetite and magnesioferrite, other minerals, such as ilmenite and V-Ti magnetite, were likely to cause secondary pollution. The subsequent adjustment to alkaline state for chemical precipitation of leached Mn was needed. Pyrite showed relatively high leachability in hazardous elements (especially Pb), which should be carefully evaluated before its actual application in electro-Fenton process.
Iron oxides such as wustite (FeO), hematite (α-Fe2O3), maghemite (γ- Fe2O3), and magnetite (Fe3O4) have received a momentous amount of interest over the past decades as efficient adsorbent/catalysts for different environmental applications. Besides, existing in various types, each oxide of iron has different phases with distinct properties suitable for environmental catalysis. These classes of materials are relative abundant, non-toxic, safe to handle and can be easily prepared via different routes. Because of their high catalytic activity, redox and magnetic properties, these materials have been applied as heterogeneous catalyst in various advanced oxidation processes (AOPs) such as catalytic ozonation, Fenton oxidation, electrocatalysis, photocatalysis, and sulfate radical-based AOPs as well as adsorption of some contaminants. In this chapter, the synthesis, properties and applications of different types of iron oxides based heterogeneous catalysts for the remediation of pollutants from wastewater were enumerated. It will be of great interest for researchers in environmental engineering.
At present, electrochemical advanced oxidation processes (EAOPs) have attracted extensive attention to treat refractory organic pollutants effectively because of their high efficiency and strong oxidation ability. Highly efficient hydrogen peroxide (H2O2) production through electrochemical oxygen reduction reaction (ORR) is of great significance for degrading organic pollutants. Due to the excellent gas-liquid-solid three-phase structure, gas diffusion electrodes (GDEs) present high cost-effectiveness, low energy consumption and high oxygen utilization efficiency in 2e⁻ ORR process. Recently, GDEs as the cathode for EAOPs applications have progressively become a popular research field. Herein, an in-depth overview of multifarious GDEs currently available in EAOPs for environmental remediation was presented. In this review, the preparation, evaluation and modification methods of GDEs were summarized. Particular emphasis was placed on the applications of GDEs-based cathodes for H2O2 generation and pollutants degradation by EAOPs, mainly including the effects and current development of fabrication method, evaluation parameters and cathode modification. Moreover, to expand the practical application in electro-Fenton, photoelectro-Fenton and iron-free Fenton-like process, typical reactors designs and electrochemical processes using GDEs were further highlighted. Finally, the prospect of GDEs for H2O2 production and water treatment were proposed.
In electrochemical advanced oxidation processes (EAOPs), a series of transition metal encapsulated nitrogen-doped carbon nanotubes ([email protected], M=Fe, Co, Ni, Cu) as bifunctional cathodes were synthesized to compare and uncover their activity trends, fulfilling the self-sufficient electrocatalytic degradation. The sulfamethazine (SMT) degradation activity trends were follows: [email protected]>[email protected]>[email protected]>[email protected] cathode at pH≤7, while the [email protected] cathode exhibited the highest activity at pH 9 due to the more ¹O2 and atomic H*. In-situ Fourier transformed infrared (FTIR) spectroscopy and density functional theory (DFT) calculation suggested that the atomic H* was easier to generate under the action of pyridinic N on [email protected] cathode. Overall, various pollutants degradation on [email protected] cathode performed with good stability with low leaching iron (0.12 mg L⁻¹) and low energy consumption (<0.3 kWh∙log⁻¹∙m⁻³). This study sheds light on different mechanisms of reactive species production on [email protected] cathode, thus providing guidance for the selectivity between [email protected] via active species and pollutants.
Iron alginate beads (Fe-Alg) were prepared, characterized and implemented for the degradation of amoxicillin (AMX) by the heterogeneous electro-Fenton process using a graphite cathode recovered from used batteries. Scanning electron microscopy (SEM) showed that (Fe-Alg) beads have a spherical shape and the results of energy dispersive spectrometric (EDS) revealed the presence of iron in (Fe-Alg). Optimization of the operating parameters showed that a complete degradation of AMX was achieved within 90 min of heterogeneous electro-Fenton treatment by operating under these conditions: initial AMX concentration: 0.0136 mM, I = 600 mA, [Na2SO4] = 50 mM, pH = 3, T = 25 °C, ω = 360 rpm. The corresponding chemical oxygen demand (COD) abatement was 50%. Increasing the contact time increased the COD abatement to 85.71%, after 150 min of heterogeneous electro-Fenton treatment. The results of the kinetic study by using nonlinear methods demonstrated that the reaction of AMX degradation obeyed to a pseudo-second-order kinetic. Iron content of 4.63% w/w was determined by the acid digestion method. After 5 cycles of use, the Alg-Fe catalyst depletion was only 8%. Biodegradability was remarkably improved after electro-Fenton pretreatment, since it increased from 0.07 initially to 0.36. The heterogeneous electro-Fenton process had efficiently eliminated AMX and it increased the biodegradability of the treated solution. HIGHLIGHTS
The heterogeneous electro-Fenton process was used for the degradation of amoxicillin (AMX).;
The Fe-Alg catalyst has proved its efficiency and stability.;
The kinetic model of the AMX degradation obeyed to a pseudo-second-order.;
The COD abatement and removal yield of AMX were 50% and 100% respectively.;
The heterogeneous electro-Fenton pretreatment improved the biodegradability of the AMX from 0.07 initially to 0.36.;
The mineral particles in sediment could affect polystyrene microplastics (PS-MPs) prosperity through physical and chemical interactions. Pyrite with semiconducting properties is the most abundant metal sulfide mineral in the sediments of lake and river mouths. The widespread sunlight and the coexistence of PS-MPs and pyrite in lake or river water due to frequently water fluctuation is a typical photoaging environment for PS-MPs. The oxidation of reactive oxygen species (ROS) generated from pyrite would degrade the PS-MPs in theory. However, researches about photoaging of PS-MPs mediated by pyrite are paucity. Here, we investigated the photoaging process of PS-MPs affected by pyrite under simulated light condition. Remarkably, surface morphology of PS-MPs mediated by pyrite was broken. And the oxygen-containing functional group of PS-MPs increased, as revealed by Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and contact angle test. 2D-COS analysis showed photoaging of PS-MPs with pyrite happened in the following order: C-H > C=C > C=O > C-O > OH. The photoaging of PS-MPs and transformation of intermediate were accelerated by ROS (O2·⁻, ·OH and ¹O2) generated from pyrite. The free ·OH may play a major role in the promotion. Because the interfacial ROS reactions on pyrite surface were limited due to the electrostatic repulsion between pyrite and PS-MPs. The study explored photoaging behavior of PS-MPs accelerated by pyrite, which could be helpful for understanding photon-induced redox chemistry on PS-MPs via widespread sulfide metal minerals on earth's surface and providing further information to assess potential risks of PS-MPs.
Proper treatment of wastewater is one of the key issues to the sustainable development of human society, and people have been searching for high-efficiency and low-cost methods for wastewater treatment. This article reviews recent studies about pyrite-mediated advanced oxidation processes (AOPs) in removing refractory organics from wastewater. The basic information of pyrite and its characteristics for AOPs are first introduced. Then, the performance and mechanisms of pyrite-mediated Fenton oxidation, electro-Fenton oxidation, and persulfate oxidation processes are carefully reviewed and presented. Natural pyrite is an abundant low-cost heterogeneous catalyst for AOPs, and the slow release of Fe²⁺ and the self-regulation of solution pH are highlighted characteristics of pyrite-mediated AOPs. In AOPs, the interaction between Fe³⁺ and pyrite facilitates the Fe²⁺ regeneration and the Fe²⁺/Fe³⁺ cycle. Making pyrite into nanoparticles, assisting by ultrasound and light irradiation, and adding exogenous Fe³⁺, organic chelating agents, or biochar is effective to enhance the performance of pyrite-mediated AOPs. Based on the analyses of those pyrite-mediated AOPs and their enhancing strategies, the future development directions are proposed in the aspects of toxicity research, mechanism research, and technological coupling.
In this work, the combination of two advanced oxidation processes, electro-Fenton (hydroxyl radical ●OH generated by reactions on cathode) and anodic oxidation (●OH produced directly on anode), in the same reactor was studied to evaluate the treatment of methylene blue (MB) dye in aqueous solutions. This electrochemical system was equipped with a commercial carbon felt cathode (9.5cm 12cm), lead dioxide-coated titanium anode (10 12cm), direct current (DC) and continuously aerated. The effects of operating parameters such as pH, applied current (I), catalyst concentration ([Fe2+]) and MB concentration (C0) on MB removal efficiency were investigated through monitoring MB concentration at different times by spectrophotometric method. An optimal process was achieved at the condition of [Fe2+] = 0.1 mM; pH 3.0; [Na2SO4] = 0.05 M; i = 2.5 mA.cm-2 and after 60 minutes of electrolysis, 92.19% of MB was removed which was far higher than the figure obtained by using individually electro-Fenton (73.77%) or anodic oxidation (58.04%). These experimental results have demonstrated that the combination of electro-Fenton and anodic oxidation using Ti/PbO2 electrode is a prospective method for destruction of persistent dyes.
The reduced S-modified MIL-53(Fe) was prepared by sulfurizing MIL-53(Fe) at low temperature, which was an efficient electro-Fenton catalyst at wide pH range (3-9) for sulfamethazine (SMT) degradation. The best temperature and MIL-53(Fe)/S ratio were 350 °C and 1:2, at which the BET surface area was much enlarged. The MIL-53(Fe) surface was etched by S to many 2D nanosheets with the thickness of ~50 nm, while S2-2 replaced OH⁻ to coordinate with Fe²⁺ and increased the Fe²⁺ content, which improved the catalytic performance. Even at initial pH of 7.0, the SMT removal was 95.8%, and the rate constant (k) in the Hetero-EF process was 16-folds of that in the Homo-EF process. The turnover frequency (TOFd) value of MIL-53(Fe)/S(1:2)-350 was 0.48 L g⁻¹ min⁻¹, which was 6.8 times that of commercial FeS2. The S2-2in catalyst adjusted the pH superfast, and promoted the generation of Fe²⁺ and thus efficiently activating H2O2 to form surface ·OH, which was verified to be the main radical by EPR and radical scavenger experiments. This catalyst showed promising prospect for environmental application and could be regenerated by sulfidation method. S-doped MIL-53(Fe) was an excellent pH regulator, thus promoting promising application in Hetero-EF processes.
As an important advanced oxidation process, electro-Fenton (EF) has gained considerable attention owing to its impressive ability for the degradation of refractory organic pollutants. Over the past few years, metal-organic frameworks (MOFs) have received widespread interest due to their unique merits such as large surface area, tunable pore structure and abundant active sites. MOFs derivatives with similar structural characteristics possess additional advantages compared to original MOFs, which further broadens the applications of MOFs. Particularly, MOFs-based materials have been extensively used in EF process recently and this research area is rapidly growing. This article presents a timely and comprehensive overview of MOFs and their derivatives as catalysts for EF process in water purification. We firstly reviewed synthetic methods of MOFs for EF process and displayed the advantages of MOFs derivatives. Representative research on MOFs, MOFs composites and their derivatives for EF process were then summarized. The reaction mechanisms in the EF process for elimination of various contaminants (including antibiotics, herbicides, and dyes) with MOFs-based materials as catalysts were described. Finally, an outlook on the current challenges and promising opportunities in this research area were discussed. This review should be of value in facilitating MOFs-based materials to become a competitive choice as EF catalysts for water purification.
Advanced oxidation processes (AOPs) constitute important, promising, efficient, and environmental-friendly methods developed to principally remove persistent organic pollutants (POPs) from waters and wastewaters. Generally, AOPs are based on the in situ generation of a powerful oxidizing agent, such as hydroxyl radicals (•OH), obtained at a sufficient concentration to effectively decontaminate waters. This critical review presents a precise and overall description of the recent literature (period 1990–2012) concerning the main types of AOPs, based on chemical, photochemical, sonochemical, and electrochemical reactions. The principles, performances, advantages, drawbacks, and applications of these AOPs to the degradation and destruction of POPs in aquatic media and to the treatment of waters and waste waters have been reported and compared.
In recent years, new advanced oxidation processes based on the electrochemical technology, the so-called electrochemical advanced oxidation processes (EAOPs), have been developed for the prevention and remediation of environmental pollution, especially focusing on water streams. These methods are based on the electrochemical generation of a very powerful oxidizing agent, such as the hydroxyl radical ((•)OH) in solution, which is then able to destroy organics up to their mineralization. EAOPs include heterogeneous processes like anodic oxidation and photoelectrocatalysis methods, in which (•)OH are generated at the anode surface either electrochemically or photochemically, and homogeneous processes like electro-Fenton, photoelectro-Fenton, and sonoelectrolysis, in which (•)OH are produced in the bulk solution. This paper presents a general overview of the application of EAOPs on the removal of aqueous organic pollutants, first reviewing the most recent works and then looking to the future. A global perspective on the fundamentals and experimental setups is offered, and laboratory-scale and pilot-scale experiments are examined and discussed.
The degradation of 230 mL of a 0.6-mM sulfanilamide solution in 0.05 M Na2SO4 of pH 3.0 has been studied by electro-Fenton process. The electrolytic cell contained either a Pt or boron-doped diamond (BDD) anode and a carbon-felt cathode. Under these conditions, organics are oxidized by hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton’s reaction between initially added (and then electrochemically regenerated) Fe2+ and cathodically generated H2O2. From the decay of sulfanilamide concentration determined by reversed-phase liquid chromatography, an optimum Fe2+ concentration of 0.20 mM in both cells was found. The drug disappeared more rapidly using BDD than Pt, and, in both cases, it was more quickly removed with raising applied current. Almost total mineralization was achieved using the BDD/carbon-felt cell, whereas the alternative use of Pt anode led to a slightly lower mineralization degree. In both cells, the degradation rate was accelerated at higher current but with the concomitant fall of mineralization current efficiency due to the greater increase in rate of the parasitic reactions of hydroxyl radicals. Reversed-phase liquid chromatography allowed the identification of catechol, resorcinol, hydroquinone, p-benzoquinone, and 1,2,4-trihydroxybenzene as aromatic intermediates, whereas ion exclusion chromatography revealed the formation of malic, maleic, fumaric, acetic, oxalic, formic, and oxamic acids. NH4
+, NO3
−, and SO4
2− ions were released during the electro-Fenton process. A plausible reaction sequence for sulfanilamide mineralization involving all detected intermediates has been proposed. The toxicity of the solution was assessed from the Vibrio fischeri bacteria luminescence inhibition. Although it acquired its maximum value at short electrolysis time, the solution was completely detoxified at the end of the electro-Fenton treatment, regardless of the anode used.
Electrochemical Fenton treatment of aromatic pollutants in aqueous medium always leads to the formation of short-chain carboxylic acids, which account for the slower degradation rate at the final stages of the process. In order to gain further insight into the fate of such compounds, bulk electrolyses of 200ml aqueous solutions of eleven C1–C4 carboxylics, namely formic, glyoxylic, oxalic, acetic, glycolic, pyruvic, malonic, maleic, fumaric, succinic and malic acid have been carried out by electro-Fenton process with 0.1mM Fe2+ as catalyst, at room temperature and pH 3.0, applying a constant current and using an open and undivided cell equipped with a carbon-felt cathode and a Pt anode. In situ cathodic electrogeneration of Fenton's reagent leads to the formation of the very oxidizing species hydroxyl radical (OH) in the medium, allowing the degradation and total mineralization of all carboxylics studied. Various goals have been accomplished: (a) identification of the degradation intermediates for each carboxylic acid and study of their time course, (b) discussion and proposal of the reaction mechanisms under the action of OH/O2, (c) analysis of the decay kinetics and determination of the absolute rate constants, which agree well with those available in literature for processes involving OH, (d) verification of the great oxidation ability of the process to degrade mixtures containing all the carboxylics, upon variation of some experimental parameters such as current, concentration and cathode dimensions and, finally, (e) elucidation of a detailed reaction sequence for their mineralization, indicating the plausible pre-eminent pathways.
Here we demonstrate that anodic oxidation with a boron-doped diamond (BDD) electrode can be applied to the remediation of wastewaters containing indigo carmine. This environmentally friendly method decontaminates completely acid and alkaline aqueous solutions of this dye. The degradation rate increases with increasing current and dye concentration. Indigo carmine is more rapidly removed in alkaline than in acid medium, but its kinetics does not follow a defined reaction order. Isatin 5-sulfonic acid is the main aromatic product formed. Oxalic and oxamic acids are generated as ultimate carboxylic acids. The nitrogen of the dye is converted into NH4
+ and NO3
−.
Over the past few years, pharmaceuticals are considered as an emerging environmental problem due to their continuous input and persistence to the aquatic ecosystem even at low concentrations. Advanced oxidation processes (AOPs) are technologies based on the intermediacy of hydroxyl and other radicals to oxidize recalcitrant, toxic and non-biodegradable compounds to various by-products and eventually to inert end-products. The environmental applications of AOPs are numerous, including water and wastewater treatment (i.e. removal of organic and inorganic pollutants and pathogens), air pollution abatement and soil remediation. AOPs are applied for the abatement of pollution caused by the presence of residual pharmaceuticals in waters for the last decade. In this light, this paper reviews and assesses the effectiveness of various AOPs for pharmaceutical removal from aqueous systems.
Our previous report based on a batch reactor system for the Advanced Fenton Process (AFP) showed that pH, hydrogen peroxide and the organic substances treated are among the most important factors affecting the oxidation efficiency. As an extended study towards its potential commercialisation, this paper reports the effects of the main process parameters including those relating to a new laboratory scale AFP flow-through system. In order to systemise and correlate the results, the Taguchi experimental design method was used. Total organic carbon (TOC) removal was utilised as the measure of the oxidation efficiency and it was found that the removal of phenol from aqueous solution at pH 2.0 and 2.5 was very similar but hydrogen peroxide supply significantly affected the TOC removal with the change of flow rate from 14.4 ml/h to 60 ml/h. Also, the initial concentration of phenol was a highly significant factor, with higher concentrations resulting in a lower TOC removal rate. The temperature effects in the range of 14-42 degrees C were investigated and it was found that there was accelerated oxidation of phenol in the early stages but after 90 min there was no significant difference between the results. Sonication with a bath type sonicator resulted in relatively small enhancements of TOC removal but further studies with cup-horn sonication showed that TOC removal increased with higher intensity of sonication.
The study described examines the possibility of determining hydrogen in slags, including oxyfluoride slags, through reductive fusion in a stream of carrier gas, using pulsed heating. Composition of the gas phase was determined by calculating thermodynamic characteristics of reactions involving carbon, water, and calcium fluoride in a range of 1000-3000 degree K.
Olive oil mill wastewater (OMW) was tested for phytotoxicity on seed germination and seedling growth of radish and wheat. The most potent inhibition was observed with the reverse osmosis fraction, from this, 17 polyphenols with molecular weight less than 300 Daltons were isolated by chromatographic processes and identified on the basis of their spectroscopic features. In seed bioassays, the inhibitory activity of each polyphenol was much lower than that observed for the original fraction and the mixture of the pure 17 polyphenols present in reverse osmosis fraction had less effect on seed germination. Thus, OMW phytotoxicity could be due to a synergic action of polyphenols with other unidentified substances present in the wastewater.
Degradation of off-gas toluene from a toluene reservoir and a soil vapor extraction (SVE) process was investigated in a continuous pyrite Fenton system. The removal of off-gas toluene from the toluene reservoir was >95% by 8h in the pyrite Fenton system, while it was ∼97% by 3h in classic Fenton system and then rapidly decreased to initial level by 8h. Continuous consumption of low Fe(II) concentration dissolved from pyrite surface (0.05-0.11mM) was observed in the pyrite Fenton system, which can lead to the effective and successful removal of the gas-phase toluene due to stable production of OH radical (OH). Inhibitor and spectroscopic test results showed that OH was a dominant radical that degraded gas-phase toluene during the reaction. Off-gas toluene from the SVE process was removed by 96% in the pyrite Fenton system, and remnant toluene from rebounding effect was treated by 99%. Main transformation products from toluene oxidation were benzoic acid (31.4%) and CO2 (38.8%) at 4h, while traces of benzyl alcohol (1.3%) and benzaldehyde (0.7%) were observed. Maximum operation time of continuous pyrite Fenton system was estimated to be 56-61d and its optimal operation time achieving emission standard was 28.9d.
In this study, the Fe3O4 magnetic nanoparticles (MNPs) were synthesized as heterogeneous catalysts to effectively degrade bisphenol A (BPA). The properties of the synthesized catalysts were characterized by Brunnaer–Emmett–Teller (BET), X-ray powder diffraction (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The results indicated that the Fe3O4 MNPs appeared to be roughly spherical shapes and their average size was 10–20 nm. The catalytic capacity of MNPs in US + Fe3O4 + H2O2 system with different pH conditions, H2O2 concentrations and MNPs doses was investigated. It was found that the OH radicals were promptly generated due to the catalysis of the Fe3O4 MNPs. BPA could be degraded within a wide pH range from 3 to 9, and the degradation efficiencies were remarkably enhanced by ultrasound. The apparent rate constants were 8.31 × 10−3, 7.96 × 10−3 and 5.64 × 10−3 min−1, respectively, when the pH values were 3, 7 and 9, respectively. The removal efficiencies of BPA were all over 95%. About half total organic carbon (TOC) in solution was eliminated under neutral condition by sono-Fenton process. Furthermore, the results of stability and reusability demonstrated that the Fe3O4 MNPS were promising in the treatment of wastewater with refractory organics.
Independent solutions of 2.5 L of the azo dyes Acid Red (AR88) and Acid Yellow (AY9) in Na2SO4 with low contents of catalytic Fe2+ at pH 3.0 have been degraded by electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) using a recirculation flow plant containing a one-compartment cell with a boron-doped diamond (BDD) anode and an air-diffusion electrode (ADE) as cathode, each one of 20 cm2, coupled with a solar photoreactor. The EF process yields rapid decolorization, but poor total organic carbon (TOC) removal because azo dyes are oxidized with hydroxyl radicals formed at the BDD anode from water oxidation and in the bulk from Fenton's reaction between added Fe2+ and H2O2 generated at the ADE cathode, leading to persistent carboxylic acids like oxalic acid that is the major component of final electrolyzed solutions. The quick photolysis of Fe(III)-oxalate complexes by UV light of solar irradiation explains the higher oxidation power of SPEF giving almost total mineralization. The incident UV light also photodecomposes several N-derivatives favoring the release of NH4+ ion in front of NO3− ion and the loss of volatile N-compounds. The effect of current density (25–150 mA cm−2), Fe2+ concentration (up to 0.8 mM) and dye concentration (between 50 and 200 mg L−1 TOC) on the degradation rate, mineralization degree, mineralization current efficiency and specific energy cost of the SPEF treatment is examined. The application of this technology is more viable at lower current density and higher azo dye content operating at optimum 0.5 mM Fe2+, since greater efficiency and smaller specific energy cost are obtained for the mineralization process.
This article reports the complete mineralization of atrazine. Atrazine has been the most widely used s-triazine herbicide. Atrazine occurs in natural waters and presents a potential danger for public health because atrazine is considered as an endocrine disruptor. The use of chemical, photochemical and photocatalytic advanced oxidation processes (AOPs) to decontaminate waters containing atrazine only allowed its conversion into the cyanuric acid as ultimate end products, since it cannot be completely degraded by hydroxyl radicals (•OH) produced by these techniques. The same behavior was previously reported for anodic oxidation and electro-Fenton with Pt anode, although better performances were found using boron-doped diamond (BDD) anode but without explaining the role of generated •OH. Here, the oxidative action of these radicals in such electrochemical AOPs has been clarified by studying the mineralization process and decay kinetics of atrazine and cyanuric acid in separated solutions by anodic oxidation with BDD and electro-Fenton with Pt or BDD anode using an undivided cell with a carbon-felt cathode under galvanostatic conditions. Results showed that electro-Fenton with BDD anode was the more powerful treatment to degrade both compounds. Almost total mineralization, 97% total organic carbon (COT) removal, of atrazine was only feasible by this method with a faster removal of its oxidation intermediates by •OH formed at the BDD surface than that formed in the bulk from Fenton reaction, although the latter process caused a more rapid decay of the herbicide. Cyanuric acid was much slowly mineralized mainly with •OH produced at the BDD surface, and it was not degraded by electro-Fenton with Pt anode. These results highlight that electrochemical advanced oxidation processes (EAOPs) using a BDD anode are more powerful than the classical electro-Fenton process with Pt or PbO2 anodes.
Detoxification and biodegradation of olive oil mill wastewater (OOMW) and toxicity (antibacterial effect) of untreated and treated (detoxified with Trametes versicolor) OOMW on a soil bacterium, P. aeruginosa were determined. T. versicolor biodegraded and detoxified OOMW. This research showed that T. versicolor can be satisfactorily used for biodegradation and detoxification of this waste.
Electrochemical degradation of toxic and persistent organic pollutant 2-Nitrophenol (2-NP) in acidic medium of pH 3 has been comparatively studied by electrochemical advanced oxidation processes (EAOPs) such as anodic oxidation using BDD anode (AO-BDD), electro-Fenton (EF-Pt) and anodic oxidation coupled to electro-Fenton (EF-BDD) processes under galvanostatic electrolysis conditions. The effect of current density and 2-NP initial concentration on the degradation rate and solution TOC removal efficiency was studied. The oxidation power of these processes has been comparatively studied in a one compartment cell with platinum (Pt) or boron doped diamond (BDD) anode. Results obtained show that acidic solutions of 2-NP can be efficiently mineralized by all EAOPs under examination, with increasing oxidation/mineralization power in order AO-Pt
The degradation of 10L of 157mgL−1 paracetamol solutions in 0.05M Na2SO4 has been studied by the solar photoelectro-Fenton (SPEF) method. A solar flow plant with a Pt/air-diffusion electrochemical cell and a compound parabolic collector (CPC) photoreactor was used operating under recirculation mode at a liquid flow of 180Lh−1 with an average UV irradiation intensity of about 32Wm−2. A central composite rotatable design coupled with response surface methodology was applied to optimize the experimental variables. Optimum SPEF treatment was achieved by applying a current of 5A, 0.40mM Fe2+ and pH 3.0 at 120min of electrolysis, being reduced total organic carbon (TOC) by 75%, with an energy cost of 93kWhkg−1 TOC (7.0kWhm−3) and a mineralization current efficiency of 71%. Initial N was partially converted into NH4+ ion. Under these optimized conditions, paracetamol decays followed a pseudo first-order kinetics. HPLC analysis of the electrolyzed solution allowed the detection of hydroquinone, p-benzoquinone, 1,2,4-trihydroxybenzene, 2,5-dihydroxy-p-benzoquinone and tetrahydroxy-p-benzoquinone. All aromatics were destroyed by the attack of OH. Maleic, fumaric, succinic, lactic, oxalic, formic and oxamic acids were identified as generated carboxylic acids, which form Fe(III) complexes that are quickly photodecarboxylated under UV irradiation of sunlight. A reaction sequence involving all the detected byproducts was proposed for the SPEF degradation of paracetamol.
The removal of the anthraquinone dye Alizarin Red S (AR) has been investigated by electro-Fenton process using a commercial graphite-felt to electrogenerate in situ hydrogen peroxide and regenerate ferrous ions as catalyst. The effect of operating conditions such as applied current, catalyst concentration, and initial dye content on AR degradation has been studied. AR decay kinetic, the evolution of its oxidation intermediates and the mineralization of the aqueous solutions were monitored during the electrolysis by UV–Vis analysis and TOC measurements. The experimental results showed that AR was completely removed by the reaction with OH radicals generated from electrochemically assisted Fenton's reaction, and the decay kinetic always follows a pseudo-first-order reaction. Applying a current of 300mA and with catalyst concentration of 0.2mM Fe2+, 95% of the initial TOC was removed in 210min of electrolysis, meaning the almost complete mineralization of the organic content of the treated solution.
The vast majority of olive oil production (>98%) occurs in the Mediterranean region, utilizing a tremendous volume of water (10–30millionm3) in an area of the world in which water resources are limited. Treatment and reuse of olive mill wastewater (OMWW) presents significant challenges both due to the nature of olive oil production (seasonal and small scale) and due to the characteristics of the wastewater (high chemical oxygen demand (COD), high phenolic content, and dark color). A number of different microorganisms (Archaea, Bacteria and fungi) and processes (aerobic or anaerobic bioreactors, composting) have been tested to treat OMWW. Aerobic bacteria have been tested primarily as an approach for removal of phytotoxic compounds from OMWW, although some studies have also focused on reduction of COD. Fungi on the other hand, have proven effective at reducing COD and toxicity. Anaerobic consortia can effectively reduce COD, but are sensitive to phenolics in OMWW. Biological processes provide some of the most viable options for the treatment of OMWW. Effective application of these techniques, yielding significant reductions in COD, phenolics, and color, will allow safe and economical disposal of OMWW.
The dissolution of pyrite is important in the geochemical cycling of iron and sulphur, in the formation of acid mine drainage, and in the extraction of metals by bacterial leaching. Many researchers have studied the kinetics of dissolution, and the rate of dissolution has often been found to be half-order in ferric ions or oxygen. Previous work has not adequately explained the kinetics of dissolution of pyrite. The dissolution of pyrite is an oxidation-reduction reaction. The kinetics of the oxidation and reduction half-reactions was studied independently using electrochemical techniques of voltammetry. The kinetics of the overall reaction was studied by the electrochemical technique of potentiometry, which consisted of measuring the mixed potential of a sample of corroding pyrite in solutions of different compositions. The kinetics of the half reactions are related to the kinetics of the overall dissolution reaction by the condition that there is no accumulation of charge. This principle is used to derive expressions for the mixed potential and the rate of dissolution, which successfully describe the mixed potential measurements and the kinetics of dissolution reported in the literature. It is shown that the observations of half-order kinetics and that the oxygen in the sulphate product arises from water are both a direct consequence of the electrochemical mechanism. Thus it is concluded that the electrochemical reaction steps occurring at the mineral-solution interface control the rate of dissolution. Raman spectroscopy was used to analyze reaction products formed on the pyrite surface. The results indicated that small amounts of polysulphides form on the surface of the pyrite. However, it was also found that the mixed (corrosion) potential does not change over a 14-day leaching period. This indicates that even though polysulphide material is present on the surface, it does not influence the rate of the reactions occurring at the surface. Measurements of the sulphur yields as a function of electrode potential indicate that thiosulphate is not the only source of the sulphur product.
In this work, a new and highly active heterogeneous Fenton system based on iron metal and magnetite Fe0/Fe3O4 composites has been prepared by controlled reduction of iron oxides. Temperature-programmed reduction experiments with H2 showed that iron oxides, i.e. Fe2O3, FeOOH and Fe3O4, can be reduced to produce highly reactive Fe0/Fe3O4 composites with different metal to oxide ratios as determined by Mössbauer spectroscopy and powder X-ray diffraction. Mössbauer measurements revealed that these composites are reactive towards gas phase molecules and can be oxidized rapidly by O2 even at room temperature. The composites showed also very high activity for the Fenton chemistry, i.e. the oxidation of an organic model contaminant, the dye methylene blue, and the H2O2 decomposition. The best results were obtained with the composites with 47% Fe0 obtained by reduction of Fe3O4 with H2 at 400°C for 2h, which produced a very rapid discoloration with total organic carbon (TOC) removal of 75% after 2h reaction. Conversion electron Mössbauer spectroscopy (CEMS) measurements before and after H2O2 reaction showed that Fe3O4 and especially Fe0 are oxidized during the reaction. The reaction mechanism is discussed in terms of the formation of HO radicals by a Haber–Weiss initiated by an efficient electron transfer from the composite Fe0/Fe3O4 to H2O2. The higher activity of the composites compared to the pure Fe0 and iron oxides has been explained by two possible effects, i.e. (i) a thermodynamically favorable electron transfer from Fe0 to Fe3O4 producing Fe2+magnetite active for the reaction and (ii) by the formation of very reactive small particle size Fe0 and Fe3O4.
A novel cathode material, carbon sponge (CS), was investigated for treating wastewater containing the basic blue 3 (BB3) dye by electrochemical advanced oxidation processes, electro-Fenton. The efficiency of the CS electrode was comparatively discussed with carbon felt (CF) electrode for degradation of BB3. The amount of electrogenerated H2O2 by using CS electrode was three times higher than that of CF electrode. The effect of some operational parameters such as applied current value, type of supporting electrolyte, O2 flow rate, pH and temperature on the generation of H2O2 was investigated. The optimal current value for the H2O2 production was 100mA (5.6mAcm−2). The applied current, temperature and O2 flow rate have a significant effect on the amount of electrogenerated H2O2, whereas supporting electrolyte and pH of the solution have a slight affect. The degradation and mineralization of BB3 were followed by using HPLC and TOC analysis, respectively. The degradation and mineralization of BB3 using CS was faster than that of CF. At the end of eight hours electrolysis under the same conditions, 91.6% and 50.8% of the initial TOC of the system was removed by using CS and CF electrodes, respectively. The mineralization current efficiency (MCE) of CS electrode was four times higher than that of CF electrode. The results showed that the CS electrode provides an alternative cathode material for future designing of water treatment system in the electro-Fenton process.
Environmental Context. The combination of the Fenton’s reagent with electrochemistry (the electro-Fenton process) represents an efficient method for wastewater treatment. This study describes the use of this process to clean olive oil mill wastewater, which is a real environmental problem in Mediterranean countries. Contrary to the conventional methods which reduce the pollution by removing the pollutants from the wastewater, the electro-Fenton process is shown to fully destroy (mineralize) olive oil mill wastes in water without previous extraction and without addition of chemical reagents.
Abstract. Treatment of olive oil mill wastewater is one of the most important environmental problems for Mediterranean countries. This wastewater contains many organic compounds like polyphenols, which are very difficult to treat by classical techniques. An advanced electrochemical oxidation process, the electro-Fenton process, has been used as a way of removing chemical oxygen demand and colour intensity from olive oil mill wastewater. Vanillic acid, which has been selected as a model compound, and olive oil mill wastewater have been completely mineralized by the electro-Fenton process with a carbon felt cathode, using Fe2+ ions as the catalyst.
Acidic aqueous solutions of the drug paracetamol have been degraded by anodic oxidation and indirect electro-oxidation methods using an undivided electrolytic cell with a Pt anode and an O-2-diffusion cathode for H2O2 electrogeneration. Anodic oxidation yields low mineralization due to the limited production of oxidant hydroxyl radical ((OH)-O-.) from water oxidation at Pt. The presence of Cu2+ as catalyst, with and without (ultraviolet A, UVA) irradiation, slightly enhances the degradation process. In electro-Fenton, much more (OH)-O-. is produced from Fenton's reaction between added Fe2+ and electrogenerated H2O2, but stable Fe3+ complexes are formed. These species are partially photodecomposed in photoelectro-Fenton under UVA irradiation. The use of Fe2+ and Cu2+ yields fast decontamination because Cu2+ complexes are destroyed. Total mineralization of paracetamol is achieved when Fe2+, Cu2+, and UVA light are combined. The influence of current, pH, and drug concentration upon the efficiency of catalyzed methods is studied. Hydroquinone, p-benzoquinone, and carboxylic acids, such as ketomalonic, maleic, fumaric, oxalic, and oxamic, are detected as intermediates. The positive synergetic effect of all catalysts is explained by the oxidation of Cu2+-oxalato and Cu2+-oxamato complexes with (OH)-O-., along with the photodecarboxylation of Fe3+-oxalato and Fe3+-oxamato complexes by UVA light. NH4+ and NO3- are released during drug mineralization. (c) 2005 The Electrochemical Society.
Pre-treatment of olive mill wastewater (OMW) by Fenton Oxidation with zero-valent iron and hydrogen peroxide was investigated to improve phenolic compounds degradation and the chemical oxygen demand (COD) removal. Experimental procedure is performed with diluted OMW with COD 19 g/L and pH 5.2. The application of zero-valent Fe/H2O2 procedure allows high removal efficiency of pollutants from OMW. The optimal experimental conditions were found to be continuous presence of iron metal, acidic pH (2–4) and 1 M hydrogen peroxide solution. The experimental results show that the removal of 1 g of COD need 0.06 M of H2O2. At pH 1, the maximum COD removal (78%) is achieved after 1 h. Therefore, with a pH value within 2 and 4 the maximum COD removal reached 92%. Phenolic compounds are identified in treated and untreated OMW by gas chromatography coupled to mass spectrometry (GC–MS). The result shows a total degradation of phenolic compounds and an increasing biodegradability of treated OMW.
Advanced chemical, photochemical and electrochemical oxidation processes based on catalytic generation of hydroxyl radicals through Fenton's reagent are applied to remove herbicide diuron from aqueous medium. To enhance the oxidation power of Fenton's reagent, it was assisted photochemically (photo-Fenton) or electrochemically (electro-Fenton). Kinetic analysis showed that the oxidation of diuron by hydroxyl radicals follows a reaction kinetic of pseudo-first order. The apparent rate constants values and mineralization degree of different photochemical processes revealed the superiority of the photo-Fenton process in degradation rate (kinetics) and that of electro-Fenton process in cost effectiveness and process efficiency. The absolute rate constant for diuron oxidation by hydroxyl radical was determined as (4.75 ± 0.20) × 109 L mol−1 s−1 by competition kinetics method taking benzoic acid as reference compound. Electro-Fenton process exhibits a very fast degradation kinetics achieving complete removal of 0.17 mM diuron in less than 6 min. The apparent current efficiency was determined; its maximum value of 28% at 0.6 h decreases with the treatment time to 11% at 3 h, i.e., when 89% of mineralization is achieved. When 300 mA was applied, higher mineralization efficiency of 96% was achieved. The photo-Fenton process exhibits also high mineralization efficiency reaching 97% TOC removal at 5 h under optimal operating conditions. Several oxidation by-products such as 3,[3,4-dichlorohydroxyphenyl]-1,1-methylurea, 3,[3-hydroxy 4-chlorohydroxyphenyl]-1,1-methylurea, 3-[trihydroxyphenyl]-1,1-dimethylurea, 3,[3-hydoxy-4-chlorophenyl]-1,1-methylurea, 3,[3-hydroxy-4-chlorophenyl]-1,1-dimethylurea, and dichloroaniline were identified by HPLC and LC–MS analyses evidencing two sites of attack of hydroxyl radical, the first being located on the aromatic ring and the second on the dimethylurea group. Based on the identification of aromatic intermediates, carboxylic acids and chloride ion released; a plausible diuron mineralization pathway is proposed.
Several low-soluble mineral iron oxides have been studied as an iron source for the production of hydroxyl radicals via
decomposition in the presence of ferrous ions (Fenton’s reaction). In particular, this study focuses on electro-Fenton and
photoelectro-Fenton processes, using aniline as a model pollutant. The aim of this work is to spread the use of iron minerals
as catalyst in the different electrochemical wastewater treatments. Among all the iron oxides tested, magnetite
and wustite
show the more promising results. The main advantages of these minerals are that they produce lower concentrations of iron
in solution, ease of recycling the iron catalyst, and their ability to self-regulate the concentration of iron ions in solution.
Wustite and magnetite behave purely as a source of iron ions in the electro-Fenton process. But, magnetite exhibits a heterogeneous
photocatalytic effect when used as an iron source in the photoelectro-Fenton process. This new magnetite-photoelectro-Fenton
process significantly improves the pollutant removal yield (16.7% more after
of mineralization) compared to the conventional photoelectro-Fenton process. This effect is observed for two different wavelengths
in the UV range, 254 and
.
A previous contribution from our laboratory reported the formation of hydrogen peroxide (H2O2) upon addition of pyrite (FeS2) to O2-free water. It was hypothesized that a reaction between adsorbed H2O and Fe(III), at a sulfur-deficient defect site, on the pyrite surface generates an adsorbed hydroxyl radical (OH•). The combination of two OH• then produces H2O2. In the present study, we show spectroscopic evidence consistent with the conversion of Fe(III) to Fe(II) at defect sites, the origin of H2O2 from H2O, and the existence of OH• in solution. To demonstrate the iron conversion at the surface, X-ray photoelectron spectroscopy (XPS) was employed. Using a novel mass spectrometry method, the production of H2O2 was evaluated. The aqueous concentration of OH• was measured using a standard radical scavenger method. The formation of OH• via the interaction of H2O with the pyrite surface is consistent with several observations in earlier studies and clarifies a fundamental step in the oxidation mechanism of pyrite.
A modified Fenton reagent, using solid pyrite in the place of soluble ferrous iron salt, has been used to clean-up pure water spiked with 2,4,6-trinitrotoluene (TNT). Water treatment was conducted at pH 3 with 1.8–28.6 mM Fe (II) (as pyrite) + 0.015-0.029 M of H2O2 and compared with Classic Fenton (CF) reaction: 1.8 mM Fe (II) (as ferrous sulfate) + 0.029-0.29 M H2O2. All experiments were conducted in the dark and in the light by using an artificial light source of 200-W. The pseudo-first order rate constant, k, of TNT degradation did not significantly increased as a function of peroxide addition like in CF reagent, where all Fe (II) was in solution. When both reagents were used at the concentrations of 1.8 mM Fe (II) + 0.029 M H2O2 complete oxidation of TNT with modified Fenton reagent was slower respect to classic Fenton reagent (48 h vs. 24 h). However mineralization of TNT with 1.8 mM Fe(II) from pyrite + 0.029 M H2O2 under Dark/Light conditions was of the same order of magnitude ( %) as with CF using a 10 times higher concentration of peroxide (0.29 M H2O2). Even though reuse of oxidized pyrite after a first oxidation treatment, prolonged the time of TNT disappearance from a second solution (48 h vs 24 h with 5.4 mM Fe2+ from pyrite + 0.029 M H2O2) the extent of mineralization remained unvaried (− 45%).
The catalytic behavior of the Fe3+/Fe2+ system in the electro-Fenton degradation of the antimicrobial drug chlorophene has been studied considering four undivided electrolytic cells, where a Pt or boron-doped diamond (BDD) anode and a carbon felt or O2-diffusion cathode have been used. Chlorophene electrolyses have been carried out at pH 3.0 under current control, with 0.05 M Na2SO4 as supporting electrolyte and Fe3+ as catalyst. In these processes the drug is oxidized with hydroxyl radical (OH) formed both at the anode from water oxidation and in the medium from electrochemically generated Fenton's reagent (Fe2+ + H2O2, both of them generated at the cathode). The catalytic behavior of the Fe3+/Fe2+ system mainly depends on the cathode tested. In the cells with an O2-diffusion cathode, H2O2 is largely accumulated and the Fe3+ content remains practically unchanged. Under these conditions, the chlorophene decay is enhanced by increasing the initial Fe3+ concentration, because this leads to a higher quantity of Fe2+ regenerated at the cathode and, subsequently, to a greater OH production from Fenton's reaction. In contrast, when the carbon felt cathode is used, H2O2 is electrogenerated in small extent, whereas Fe2+ is largely accumulated because the regeneration of this ion from Fe3+ reduction at the cathode is much faster than its oxidation to Fe3+ at the anode. In this case, an Fe3+ concentration as low as 0.2 mM is required to obtain the maximum OH generation rate, yielding the quickest chlorophene removal. Chlorophene is poorly mineralized in the Pt/O2 diffusion cell because the final Fe3+–oxalate complexes are difficult to oxidize with OH. These complexes are completely destroyed using a BDD anode at high current thanks to the great amount of OH generated on its surface. Total mineralization is also achieved in the Pt/carbon felt and BDD/carbon felt cells with 0.2 mM Fe3+, because oxalic acid and its Fe2+ complexes are directly oxidized with OH in the medium. Comparing the four cells, the highest oxidizing power regarding total mineralization is attained for the BDD/carbon felt cell at high current due to the simultaneous destruction of oxalic acid at the BDD surface and in the bulk solution.
Olive oil vegetation waters (VW) were highly toxic to both phytopathogenic Pseudomonas syringae (Smith, Yung et al.) pv. savastanoi (Gram-negative) and Corynebacterium michiganense (Gram-positive) and showed bactericidal activity in their original concentration (in raw form). Among the main polyphenols, present in the waste waters, methylcatechol proved to be the most toxic to Ps. savastanoi at 10−4 mol 1−1, and also demonstrated bactericidal activity, while on Coryne. michiganense it was only slightly active; catechol and hydroxytyrosol were less active on Ps. savastanoi, but inactive on Coryne. michiganense; tyrosol and its synthetic isomers 1,2- and 1,3-tyrosol were completely inactive on both bacteria. Among the derivatives of VW polyphenols considered, acetylcatechol and guaiacol were selectively toxic for Ps. savastanoi, while o-quinone was strongly toxic for both bacteria. The minor carboxylic polyphenols of VW at 10−4 mol 1−1 were all inactive on the bacteria. VW, catechol, 4-methylcatechol and the less abundant carboxylic polyphenols proved to be toxic on Hep2 human cells. Finally the possibility of using the active polyphenols in agriculture in an integrated pest management program for the protection of the olive plant is discussed.
Olive mill wastewaters are toxic for plants and microbes due to their high polyphenol content. We studied the effect of agricultural soil as a natural catalyst to promote polyphenol oxidation and polymerization, and in turn detoxify olive mill wastewaters. We show that model polyphenols are fully converted in soil slurries. Their products show no toxicity to the growth of a typical soil bacterium, Bacillus cereus, and reduced phytotoxicity in germination tests with English cress seeds. Those findings are promising for the sustainable treatment of olive wastewater in aerated soil slurries.
Oxidative degradation of atrazine by hydroxyl radicals (OH) was studied in aqueous medium. OH were formed in situ from electrochemically generating Fenton's reagent by an indirect electrochemical advanced oxidation process. Identification and evolution of seven main aromatic metabolites and four short-chain carboxylic acids were performed by using liquid chromatography analyses. Total organic carbon (TOC) and ionic chromatography were used in order to evaluate the mineralization efficiency of treated aqueous solutions. A high mineralization rate of 82% (never reported until now) was obtained. The oxidative degradation of cyanuric acid, the ultimate product of atrazine degradation, was highlighted for the first time. The absolute rate constant of the reaction between atrazine and hydroxyl radicals was evaluated by competition kinetics method as (2.54 ± 0.22) × 109 M−1 s−1. Considering all oxidation reaction intermediates and end products a general reaction sequence for atrazine degradation by hydroxyl radicals was proposed.
A very detailed scheme for the Fe3+-catalyzed electro-Fenton mineralization of malachite green as a model triarylmethane dye is presented. Bulk electrolyses of 250-mL aqueous solutions of 0.5 mM malachite green with 0.2 mM Fe3+ as catalyst have been carried out at room temperature and pH 3.0 under constant current in an undivided cell equipped with a graphite-felt cathode and a Pt anode to assess the performance of the electro-Fenton system. In situ electrogeneration of Fe2+ and H2O2 from quick cathodic reduction of Fe3+ and dissolved O2 (from bubbled compressed air), respectively, allows the formation of the very oxidizing species hydroxyl radical (OH) in the medium from Fenton's reaction. A pseudo-first-order decay kinetics with an apparent rate constant of k1,MG = 0.244 min−1 was obtained for total destruction of malachite green by action of OH at 200 mA, requiring 22 min for total decoloration of the solution. In the same experimental conditions, overall mineralization was reached at 540 min. Up to 15 aromatic and short-chain carboxylic acid intermediates were identified along the treatment. The evolution of current efficiency was calculated from the chemical oxygen demand (COD) removal. Based on the time course of most of the by-products and the identification of inorganic ions released, some plausible mineralization pathways are proposed and thoroughly discussed. It has been found that the electro-Fenton degradation of malachite green proceeds via parallel pathways, all of them involving primary splitting of the triaryl structure initiated by attack of OH on the central carbon, thus yielding two different N-dimethylated benzophenones. Successive cleavage of the aromatic intermediates generates oxalic acid as the ultimate short-chain carboxylic acid, whereas N-demethylation of some of them produces formic acid as well. Oxalic acid and its Fe2+ complexes, as well as formic acid, can be slowly but totally mineralized by OH.
Catechol, 4-methylcatechol, tyrosol and hydroxytyrosol were isolated and characterized as the main polyphenols from olive oil mill waste waters. In addition, the corresponding acetates were prepared. In phytotoxicity assays carried out on tomato (Lycopersicon esculentum) and vegetable marrow (Cucurbita pepo) plants, the compounds were selectively toxic, except for 4-methylcatechol and its acetate. The vegetation waters remained phytotoxic even after total extraction of the polyphenols, suggesting that other chemical products contribute to the overall phytotoxicity.
Degradation experiments using 5 mmol/l ethylenediaminetetraacetic acid (EDTA) solutions at pH 3 were performed in the presence of H2O2 and metals such as Fe2+, Fe3+, Cu2+ and mixtures of Fe2+/Cu2+ and Fe3+/Cu2+ under UV-A irradiation (366 nm)—photo-Fenton and photo-Fenton-like reactions—at different metal/EDTA concentration ratios in order to determine the best conditions for EDTA photochemical removal. Analogous dark reactions were performed for comparison. The reaction course was monitored by both EDTA and TOC determinations. Hydrogen peroxide demand was also evaluated in all cases. In terms of TOC removal, photo-Fenton-like reactions were remarkably more efficient than the analogous Fenton-like reactions. When EDTA was monitored, Fenton-like reactions showed variable performances, being more efficient with EDTA:Fe2+ and EDTA:Fe3+ ratios of 1:1. However, in these both cases, reaction rates were lower than the ones obtained under irradiation. Total mineralization ranged from 31% (Cu2+ system) to 92% (Fe2+, Fe3+, Fe3++Cu2+ and Fe2++Cu2+ systems) after 4 h of irradiation. Percentage of TOC removal was higher in the presence of iron because some photoactive intermediates were probably formed during EDTA degradation.
The mineralization of flumequine, an antimicrobial agent belonging to the first generation of synthetic fluoroquinolones which is detected in natural waters, has been studied by electrochemical advanced oxidation processes (EAOPs) like electro-Fenton (EF) and photoelectro-Fenton (PEF) with UVA light. The experiments were performed in a cell containing a boron-doped diamond (BDD) anode and an air-diffusion cathode to generate H(2)O(2) at constant current. The Fe(2+) ion added to the medium increased the solubility of the drug by the formation of a complex of intense orange colour and also reacted with electrogenerated H(2)O(2) to form hydroxyl radical from Fenton reaction. Oxidant hydroxyl radicals at the BDD surface were produced from water oxidation. A partial mineralization of flumequine in a solution near to saturation with optimum 2.0mM Fe(2+) at pH 3.0 was achieved by EF. The PEF process was more powerful, giving an almost total mineralization with 94-96% total organic carbon removal. Increasing current accelerated both treatments, but with decreasing mineralization current efficiency. Comparative treatments using a real wastewater matrix led to similar degradation degrees. The kinetics for flumequine decay always followed a pseudo-first-order reaction and its rate constant, similar for both EAOPs, raised with increasing current. Generated carboxylic acids like malonic, formic, oxalic and oxamic acids were quantified by ion-exclusion HPLC. Fe(III)-oxalate and Fe(III)-oxamate complexes were the most persistent by-products under EF conditions and their quicker photolysis by UVA light explains the higher oxidation power of PEF. The release of inorganic ions such as F(-), NO(3)(-) and in lesser extent NH(4)(+) was followed by ionic chromatography.
The electro-Fenton treatment of sulfachloropyridazine (SCP), a model for sulfonamide antibiotics that are widespread in waters, was performed using cells with a carbon-felt cathode and Pt or boron-doped diamond (BDD) anode, aiming to present an integral assessment of the kinetics, electrodegradation byproducts, and toxicity evolution. H(2)O(2) electrogeneration in the presence of Fe(2+) yielded (•)OH in the solution bulk, which acted concomitantly with (•)OH adsorbed at the anode (BDD((•)OH)) to promote the oxidative degradation of SCP (k(abs,SCP) = (1.58 ± 0.02) × 10(9) M(-1) s(-1)) and its byproducts. A detailed scheme for the complete mineralization was elucidated. On the basis of the action of (•)OH onto four different SCP sites, the pathways leading to total decontamination includes fifteen cyclic byproducts identified by HPLC and GC-MS, five aliphatic carboxylic acids, and a mixture of Cl(-), SO(4)(2-), NH(4)(+), and NO(3)(-) that accounted for 90-100% of initial Cl, S, and N. The time course of byproducts was satisfactorily correlated with the toxicity profiles determined from inhibition of Vibrio fischeri luminescence. 3-Amino-6-chloropyridazine and p-benzoquinone were responsible for the increased toxicity during the first stages. Independent electrolyses revealed that their toxicity trends were close to those of SCP. The formation of the carboxylic acids involved a sharp toxicity decrease, thus ensuring overall detoxification.
The aim of this study is to provide fundamental knowledge of the treatment of wastewater containing a non-biodegradable reactive dye (C.I. Reactive Blue 19) and/or other anthraquinone dyes by catalytic effects of iron salt known as Fenton's reagent. As an advanced oxidation method, Fenton's reagent has an advantage that it combines both oxidation and coagulation processes. The influence of the main operating parameters such as iron sulfate and hydrogen peroxide doses, solution pH, temperature, initial dye concentration and presence of different concentrations of sodium chloride and sodium sulfate has been studied systematically at a laboratory scale. The obtained results showed that the best pH value for decolorization of dye solution is 3. An increase in temperature resulted in higher removal rates. Results showed that chloride and sulfate ions have a negative impact on the decolorization of RB19 by Fenton oxidation. The increase of Fe2+ and H2O2 doses accelerated the color and COD removals until a point where further addition of Fe2+ or H2O2 became inefficient and unnecessary. A new empirical kinetic model for investigation of decolorization based on simultaneous first and second-order kinetics was derived and compared to individual first- and second-order kinetic models. The results of the mixed-order kinetics showed excellent correlation with experimental data.
Oxalic and oxamic acids are the ultimate and more persistent by-products of the degradation of N-aromatics by electrochemical advanced oxidation processes (EAOPs). In this paper, the kinetics and oxidative paths of these acids have been studied for several EAOPs using a boron-doped diamond (BDD) anode and a stainless steel or an air-diffusion cathode. Anodic oxidation (AO-BDD) in the presence of Fe(2+) (AO-BDD-Fe(2+)) and under UVA irradiation (AO-BDD-Fe(2+)-UVA), along with electro-Fenton (EF-BDD), was tested. The oxidation of both acids and their iron complexes on BDD was clarified by cyclic voltammetry. AO-BDD allowed the overall mineralization of oxalic acid, but oxamic acid was removed much more slowly. Each acid underwent a similar decay in AO-BDD-Fe(2+) and EF-BDD, as expected if its iron complexes were not attacked by hydroxyl radicals in the bulk. The faster and total mineralization of both acids was achieved in AO-BDD-Fe(2+)-UVA due to the high photoactivity of their Fe(III) complexes that were continuously regenerated by oxidation of their Fe(II) complexes. Oxamic acid always released a larger proportion of NH(4)(+) than NO(3)(-) ion, as well as volatile NO(x) species. Both acids were independently oxidized at the anode in AO-BDD, but in AO-BDD-Fe(2+)-UVA oxamic acid was more slowly degraded as its content decreased, without significant effect on oxalic acid decay. The increase in current density enhanced the oxidation power of the latter method, with loss of efficiency. High Fe(2+) contents inhibited the oxidation of Fe(II) complexes by the competitive oxidation of Fe(2+) to Fe(3+). Low current densities and Fe(2+) contents are preferable to remove more efficiently these acids by the most potent AO-BDD-Fe(2+)-UVA method.
Degradation of trichloroethylene (TCE) by Fenton reaction in pyrite suspension was investigated in a closed batch system under various experimental conditions. TCE was oxidatively degraded by OH in the pyrite Fenton system and its degradation kinetics was significantly enhanced by the catalysis of pyrite to form OH by decomposing H(2)O(2). In contrast to an ordinary classic Fenton reaction showing a second-order kinetics, the oxidative degradation of TCE by the pyrite Fenton reaction was properly fitted by a pseudo-first-order rate law. Degradation kinetics of TCE in the pyrite Fenton reaction was significantly influenced by concentrations of pyrite and H(2)O(2) and initial suspension pH. Kinetic rate constant of TCE increased proportionally (0.0030 ± 0.0001-0.1910 ± 0.0078 min(-1)) as the pyrite concentration increased 0.21-12.82 g/L. TCE removal was more than 97%, once H(2)O(2) addition exceeded 125 mM at initial pH 3. The kinetic rate constant also increased (0.0160 ± 0.005-0.0516 ± 0.0029 min(-1)) as H(2)O(2) concentration increased 21-251 mM, however its increase showed a saturation pattern. The kinetic rate constant decreased (0.0516 ± 0.0029-0.0079 ± 0.0021 min(-1)) as initial suspension pH increased 3-11. We did not observe any significant effect of TCE concentration on the degradation kinetics of TCE in the pyrite Fenton reaction as TCE concentration increased.
A study was conducted to demonstrate the advantages of electro-Fenton process and related electrochemical technologies based on Fenton's reaction chemistry. The electrochemical technology had gained significance due to its ability to prevent pollution problems. Its main advantage was its environmental compatibility, as the electron was the clean reagent. The technology also offered advantages, such as versatility, high energy efficiency, amenability of automation, and safety. It was revealed that the electrochemical technologies had the ability to decontaminate wastewaters containing a large variety of organic pollutants in a wide range of experimental conditions. All these technologies were suitable for destroying the initial pollutant and mineralize the solutions treated.
The electrogeneration of hydroxyl radicals was studied at a synthetic B-doped diamond (BDD) thin film electrode. Spin trapping was used for detection of hydroxyl radicals with 5,5-dimethyl-1-pyrroline-N-oxide and with salicylic acid using ESR and liq. chromatog. measurements, resp. The prodn. of H2O2 and competitive oxidn. of formic and oxalic acids were also studied using bulk electrolysis. Oxidn. of salicylic acid gives hydroxylated products (2,3- and 2,5-dihydroxybenzoic acids). The oxidn. process on BDD electrodes involves hydroxyl radicals as electrogenerated intermediates. [on SciFinder (R)]
Olive oil vegetation waters (VW) were highly toxic to both phytopathogenic Pseudomonas syringae (Smith, Yung et al.) pv. savastanoi (Gram-negative) and Corynebacterium michiganense (Gram-positive) and showed bactericidal activity in their original concentration (in raw form). Among the main polyphenols, present in the waste waters, methylcatechol proved to be the most toxic to Ps. savastanoi at 10(-4) mol l-1, and also demonstrated bactericidal activity, while on Coryne. michiganense it was only slightly active; catechol and hydroxytyrosol were less active on Ps. savastanoi, but inactive on Coryne. michiganense; tyrosol and its synthetic isomers 1,2- and 1,3-tyrosol were completely inactive on both bacteria. Among the derivatives of VW polyphenols considered, acetylcatechol and guaiacol were selectively toxic for Ps. savastanoi, while o-quinone was strongly toxic for both bacteria. The minor carboxylic polyphenols of VW at 10(-4) mol l-1 were all inactive on the bacteria. VW, catechol, 4-methylcatechol and the less abundant carboxylic polyphenols proved to be toxic on Hep2 human cells. Finally the possibility of using the active polyphenols in agriculture in an integrated pest management program for the protection of the olive plant is discussed.
Hydrogen peroxide was produced by direct current electrolysis using two electrodes only, a carbon felt cathode and a dimensional stabilised anode (titanium coated with RuO2), without adding any chemical. The required oxygen was supplied by water oxidation and by transfer from the atmosphere. The intensity should be maintained under a maximum value to avoid peroxide reduction. High peroxide production rate and concentration were then reached. Electroperoxidation partially removed dissolved organic carbon (DOC) contained in solutions of phenol, salicylic acid, benzoic acid and humic acids. The DOC removal in effluent of municipal sewage plant corresponded to a breakage of the double bonds. Real effluents were significantly disinfected owing to the direct effect of electric current and the indirect effect of peroxide. Moreover, a remnant effect was ensured.
The production of olive oil yields a considerable amount of waste water, which is a powerful pollutant and is currently discarded. Polyphenols and other natural antioxidants, extracted from olives during oil extraction process, partially end up in the waste waters. Experimental and commercial olive oil waste waters from four Mediterranean countries were analyzed for a possible recovering of these biologically interesting constituents. Identification and quantitation of the main polyphenols were carried out by applying HPLC-DAD and HPLC-MS methods. Representative samples of ripe olives were also analyzed at the same time to correlate, if possible, their polyphenolic profiles with those of the corresponding olive oil waste waters. The results demonstrate that Italian commercial olive oil waste waters were the richest in total polyphenolic compounds with amounts between 150 and 400 mg/100 mL of waste waters. These raw, as yet unused, matrices could represent an interesting and alternative source of biologically active polyphenols.
The partition coefficient (K(p)) of the natural phenolic antioxidant compounds in the olive fruit between aqueous and olive oil phases was determined. The antioxidants of olive oil are either present in the olive fruit or formed during the olive oil extraction process. The antioxidants impart stability to and determine properties of the oil and are valuable from the nutritional point of view. The olive oil antioxidants are amphiphilic in nature and are more soluble in the water than in the oil phase. Consequently, a large amount of the antioxidants is lost with the wastewater during processing. The determination of antioxidants was performed using HPLC, and the K(p) was estimated to be from as low as 0.0006 for oleuropein to a maximum of 1.5 for 3,4-DHPEA-EA (di-hydroxy-phenyl-ethanol-elenolic acid, oleuropein aglycon). Henry's law fitted very well to the experimental data. The partition coefficients were also estimated by applying the activity coefficients of the antioxidants in the two phases using a predictive group contribution method, the UNIFAC equation. The K(p) values estimated with UNIFAC method were of the same order of magnitude but varied from the experimental values. Nevertheless, this method may be a rough predictive tool for process optimization or design. Because the K(p) values were very low, some changes in the process are recommended in order to achieve a higher concentration of antioxidants in the oil. A temperature increase may lead to increasing the partition coefficient. Also, limiting the quantity of water during oil extraction could be a basis for designing alternative processes for increasing the antioxidant concentration in the olive oil.
Olive oil mill wastewaters (OMWs) show significant polluting properties due to their content of organic substances, and because of their high toxicity toward several biological systems. Wastewaters' toxicity has been attributed to their phenolic constituents. A chemical study of wastewaters from a Ligurian oil mill characterized phenolic products such as 1,2-dihydroxybenzene (catechol), derivatives of benzoic acid, phenylacetic acid, phenylethanol, and cinnamic acid. The OMWs were fractioned by ultrafiltration and reverse osmosis techniques and tested for toxicity on aquatic organisms from different trophic levels: the alga Pseudokirchneriella subcapitata (formerly known as Selenastrum capricornutum); the rotifer Brachionus calyciflorus; and two crustaceans, the cladoceran Daphnia magna and the anostracan Thamnocephalus platyurus. The fraction most toxic to the test organisms was that from reverse osmosis containing compounds of low molecular weight (<350 Da), and this was especially due to the presence of catechol and hydroxytyrosol, the most abundant components of the fraction.
The pre-treatment of olive mill effluents (OME) by means of coagulation-flocculation coupling various inorganic materials and organic poly-electrolytes was investigated. Tests were conducted with two different OME with chemical oxygen demand (COD) contents of 61.1 and 29.3 g/L, total suspended solids (TSS) of 36.7 and 52.7 g/L and total phenolic contents (TP) of 3.5 and 2.5 g/L, respectively. Inorganic materials such as lime, iron, magnesium and aluminum as well as four cationic and two anionic commercial poly-electrolytes were employed either alone or in various combinations and screened with respect to their efficiency in terms of TSS, TP and COD removal, the amount of sludge produced and the phytotoxicity of the resulting liquid to lettuce seeds. Coupling lime or ferrous sulphate (in the range of several g/L) with cationic poly-electrolytes (in the range of 200-300 mg/L) led to quantitative TSS removal, while COD and TP removal varied between about 10-40% and 30-80%, respectively, depending on the materials and the effluent in question; separation efficiency generally decreased with decreasing coagulant and/or flocculant concentration. To enhance organic matter degradation, iron-based coagulation was coupled with H(2)O(2), thus simulating a Fenton reaction and this increased COD reduction to about 60%. The original, untreated OME was strongly phytotoxic to lettuce seeds even after several dilutions with water; however, phytotoxicity decreased considerably following treatment with lime and cationic poly-electrolytes; this was attributed to the removal of phenols and other phytotoxic species from the liquid phase.